The resurgence of serious group A streptococcal disease which includes sepsis, toxic shock and necrotizing fasciitis has been thoroughly documented. Although other serotypes are associated with these complications, epidemiological data argue that the serotype M1 inv+ subclone was responsible for the increased incidence of toxic shock in the 1990s. Our laboratory was the first to identify the M1 clonal variant that ultimately spread to at least five continents. The overall goal of this project is to understand the role of intracellular invasion of epithelial cells in the persistence and dissemination of highly virulent strains of group A streptococci in human populations. Much of the study will focus on the molecular interactions between M protein-extracellular matrix proteins laminin and fibronectin and the epithelial cell. Experiments will define the role of M1 protein and other bacteriophage and chromosomally encoded proteins in high frequency invasion of human cells. Invasin-agonist functions will be analyzed separate from other streptococcal factors using latex beads and scanning electron microscopy. Finally, in vitro requirements for high frequency invasion will be validated using tonsil organ cultures. These studies may provide an explanation for the failure of penicillin to eradicate streptococci from the oral mucosa of children with recurrent infections.